Films of organic crystalline materials can be used in various optical applications. For example, optical waveguides made from organic material include slab waveguides in which light is confined in only one dimension, and 2-D channels of size 1 cm.times.1 .mu.m.times.1 .mu.m. In addition, cylindrical geometry devices filled inside and outside by a non-linear material and surrounded by an electrical field have been reported.
The growth of thin single crystals is discussed, for example in the reference by K. M. M. Kruse entitled "Apparatus and Method For The Growing Of Single Crystal Specimens Of Organic Substances For Infrared Spectroscopic Investigation," J. of Physics E. Scientific Instr., vol. 3, pp. 609-14, 1970, Great Britain. The crystals are grown from the melt between NaCl (or KBr) windows held at a distance of about 25 .mu.m apart by means of a thin spacer (Polyester foil). A temperature gradient is maintained first along a capillary and then along the largest dimension on the NaCl windows, resulting in a clear definition of the crystallizing zone. The crystallizing zone is slowly raised by lowering the cell along the vertical temperature gradient within a heated column.
A second reference by Pech et al. studies the growth of solid benzophenone from its own melt contained in a crucible submitted to a unidirectional temperature gradient. Pech et al., "A New Technique For Determining The Kinetics Of Crystal Growth From The Melt," J. of Crystal Growth, vol. 43, no. 1, 123-25, 1978. In this reference, a sample was placed in a 1.times.10.times.15 mm.sup.3 crucible made of glass plates. Thermal boundary conditions were imposed by two heating blocks fixed to the extremities of the crucible and connected to thermostats. The crucible is fixed to the substage of a microscope so that the moving liquid-solid interface can be maintained in coincidence with the cross-hair reticule of the objective of the microscope.
Another method for producing a crystal film is discussed in the Hattori et al. patent entitled "Method For Producing Organic Crystal Film." U.S. Pat. No. 5,385,116. In this patent, a crystal film of an organic compound is produced from a molten liquid between a pair of substrates. At least one of the pair of substrates has on a part of a surface thereof a three-dimensional geometrical structure capable of controlling the direction of crystal growth of the organic compound. The other part of the surface having the three-dimensional geometrical structure is smooth.
U.S. Pat. No. 4,793,893 to Thakur et al. entitled "Methods For The Preparation Of Thin Large-Area Single Crystals Of Diacetylenes And Polydiacetylenes" discusses a method for preparing thin large-area single crystals of diacetylene monomer. This method involves forming a liquid layer containing pure diacetylene monomer between two opposed surfaces; applying pressure to the liquid layer disposed between the two opposed surfaces; and crystallizing the liquid layer disposed between the two opposed surfaces while by evaporation the liquid layer is kept under constant pressure to form a thin large-area single crystal of pure diacetylene monomer. This patent also discusses a method for preparing a thin large-area single crystal of pure diacetylene monomer.
Notwithstanding the above mentioned references, there continues to exist a need in the art for improved structures including organic crystals and related methods for forming organic crystals.